1. Field of the Invention
The present invention relates to a semiconductor light-emitting device.
2. Description of the Prior Art
Generally, a semiconductor light-emitting device, such as a double hetero-structure laser or a light-emitting diode comprised of GaAlAs, is readily available for commercial use. However, in recent years, a semiconductor light-emitting device, such as a double hetero-structure laser or a light-emitting diode comprised of InGaAsP/InP, has also been readily available for commercial use, especially in the field of light communications systems. In InGaAsP/InP-type semiconductor light-emitting devices (lasers), a light having a wavelength in the range of 1-1.6 .mu.m is emitted. This light is suitable for light communications systems in view of the transmission loss along an optical fiber used in the device, as compared with a light emitted from the widely used GaAlAs-type laser having a wavelength of 0.85 .mu.m.
Although the InGaAsP/InP-type laser is preferable for a light communications system, it has a defect in respect to the so-called lasing threshold level-temperature characteristic. In general, the lasing threshold level must be relatively constant with respect to a wide range of ambient temperatures. In this regard, the InGaAsP/InP-type laser does not have a good characteristic, that is, the lasing threshold level sharply increases with an increase of temperature, especially when the temperature is over about 70.degree. C.
The reason for the above-mentioned defect resides briefly in a so-called "carrier leakage", that is, carriers go over a hetero-barrier and away therefrom, since the electron energy level is distributed in an active layer at a higher level with an increase of temperature. Therefore, some of the electrons having a sufficient energy level to go over the hetero-barrier leak into a clad layer. In such a case, it is considered that such a wide variation of the lasing threshold level with respect to the temperature may be enhanced by a relatively long energy relaxation time of electrons in an active layer and also by the Auger process in which an electron attains high energy through non-radiative recombination of neighbouring electrons. These mechanisms increase the number of electrons having a sufficient energy to go over the hetero-barrier.